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Denso 234-9005 Oxygen Sensor

Q: What is the difference between the upstream and downstream sensor? Can I use two of these to replace both or does this only work for upstream?

asked on September 16, 2013

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The upstream sensor threads into the pipe coming from the engine, closer to the front of the car, and the downstream sensor threads into the catalytic converter, more toward the rear of the vehicle. They are not interchangeable. WRyner · September 16, 2013 6 people found this helpful. Do you? Yes | Report I have used oreilly's website and autozone website to identify the upstream and downstream oxygen sensors. On my vehicle the part numbers are the same for both upstream and downstream. XSTEEL · March 30, 2019 5 people found this helpful. Do you? Yes | Report They are two different sensors, i recommend going to the Denso website to get the two part numbers. The upstream fails more often and the downstream one is usually cheaper. JimH · September 16, 2013 4 people found this helpful. Do you? | Report On my 03 CR-V, they are different, since I only replaced the upstream, I can't really say a lot about the downstream Kim W. · September 17, 2013 3 people found this helpful. Do you? | Report In the couple of cars I'm familiar with the upstream and the downstream sensors are different. loungingbear · September 16, 2013 3 people found this helpful. Do you? | Report upstream is the number 1 sensor it is a air fuel ratio sensor the. down stream number 2 sensor is an o2 sensor #1 is closer to engine these are different and can not be interchanged Anthony Bernacchia · September 17, 2013 4 people found this helpful. Do you? | Report Each vehicle is different in the amount of O2 sensors they have. Could be 1-4 or even more.If you know you only have two, the upstream is before the converter and the downstream is after it.You need to know which is bad before you replace it. Most parts stores can scan you vehicle and tell which one is suspect. D. Sedlak · September 16, 2013 2 people found this helpful. Do you? | Report Above/before and below/after the catalytic converter. I don't believe you can use the same sensor for both locations on most cars PJ · September 16, 2013 3 people found this helpful. Do you? | Report Upstream are close to the exhaust manifold, downstream are close to exhaust pipes and they have a larger cable. Mig Ponce… · March 11, 2021 One person found this helpful. Do you? | Report Most older O2 (oxygen) sensors were narrow band. Meaning they can only read 3 settings. (LEAN-STOIC=perfect-RICH) I hope I don't confuse with the terminology but STOIC means PERFECT ratio of fuel to air. Newer wide band O2 read in smaller increments so they are more specific. Example: They can read 1000 settings from L… see more Most older O2 (oxygen) sensors were narrow band. Meaning they can only read 3 settings. (LEAN-STOIC=perfect-RICH) I hope I don't confuse with the terminology but STOIC means PERFECT ratio of fuel to air. Newer wide band O2 read in smaller increments so they are more specific. Example: They can read 1000 settings from LEAN to RICH in little increments. No you can't just look at them and tell the difference because it's in the internal electrical design. Most older Honda's use 1 of each sensor. The upstream is NARROW BAND and downstream is WIDE BAND. Upstream is before the Cat and downstream is after the cat. The catalytic converter is where you will find the sensors. It looks like a muffler.Master ASE Mechanic and FAA Certified Aircraft Mechanic see less Most older O2 (oxygen) sensors were narrow band. Meaning they can only read 3 settings. (LEAN-STOIC=perfect-RICH) I hope I don't confuse with the terminology but STOIC means PERFECT ratio of fuel to air. Newer wide band O2 read in smaller increments so they are more specific. Example: They can read 1000 settings from LEAN to RICH in little increments. No you can't just look at them and tell the difference because it's in the internal electrical design. Most older Honda's use 1 of each sensor. The upstream is NARROW BAND and downstream is WIDE BAND. Upstream is before the Cat and downstream is after the cat. The catalytic converter is where you will find the sensors. It looks like a muffler.Master ASE Mechanic and FAA Certified Aircraft Mechanic Ordone · September 5, 2015 4 people found this helpful. Do you? | Report

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